Frequency modulation



5 Sheets-Sheet l Jan., 14, 1936. c, w; HANsELL.

FREQUENCY MODULATI'ON Filed VJune; 25, lo

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ATTONY Jam.y 14; 1936. c, W.` HANSELL 290273975 FREQUENGY MODULATLQN Filed June 25,*1950 Y SSheets-Sheet 2 Jai. 14, 1936. y C, W. HANSELL 2,027,975

FREQUENCY MODULAT I ON Filed June 25, 1930 3 Sheets-Sheet 3 INVENTOR (LARENCE W. HSELL ATTORN EY .Ps'ieaied Jaa '14, y 193s 2,027,975l .raaQUaNor Mooornrron Clarence Weston Hanseli, Port Jeferson, N,- Y.,

assigner to Radio Corporation of America, a corporation of Delaware applicati@ .time 25, 1930, sei-iai No. 463,614

as claims.

. This. invention relates tofrequency modulation and has as its principal object, the provision of new and useful means for controlling, over a desired range, the frequency of Agenerated oscillations.

` A further4 objectrof this invention is to provide electron discharge device oscillators, having long line meansfor separately fixing their natural frequencies at or beyond the extreme frequencies of the desired range, coupled together so that they'will produce, or, be forced to oscillate at, a common intermediate frequency, and means for varying the relative intensity of the energy supplied from each of the sources in 'order to vary the commonfrequency.

Long line frequency controlled oscillators are peculiarly adapted Vfor this stype of 'frequency modulation, for, they prevent undesired changes in frequency due to variations in load, biasing potentials circuit tuning and temperature. Moreover, they prevent frequency shift over large rangessthereby precluding the possibility of shift or frequency drift of the frequency modulatlon system over a range greater than that allowed to the transmitter by the Government as would rbe the case with other types of oscilla.- tors; and, in fact, allow of signaling on a channel narrower than those allotted to one circuit in present daycommunication.

' Still further objects of the present invention are to provide in radio vsignaling apparatus a transmitter' having an electron discharge device having a plurality of grids to one of which is fed modulating energy, and to the other of which lis fed energy to be modulated, and to provide cascaded highfrequency stages in which the input and output circuits of each'stage are shielded from each other and in which the stages are shielded from each other, whereby feed back is established solely through' the means provided for that purpose.`

Referring to the accompanying drawings, with the aid of which the invention is more fully described, Figures l and 2 illustrate frequency .modulation transmitters, coupled according to c the present invention, wherein periodic 4or resonant long lines are utilized for frequency control of the oscillators, and

Figures 3 and 4 are wiring diagrams of frequency .modulation transmitters wherein, for frequency control, aperiodic vlong lines are used.

Referring to Figure l, modulating energy in the form of speech` energy from transmitter l2,l

and/or keyed alternating energy from sources l and-6 is -fed over land line 8 and applied to the input circuits of electron discharge device oscillators iii, i2 oppositely varying the bias placed upon the control electrodes thereof. By virtue of the interelectrode capacity of vtubes it, i2, or byj the addition of external capacitors .across the anodes and grids thereof, they areu caused to be self oscillatory and by adjustment of the inductance vi i8 in the anode circuit and the inductances i8 and 2@ in series with the control electrodes, the regeneration is adjusted and the natural frequencies of each of oscillators I Il, l2 are caused to lie at opposite sides of a mean frequency Jand preferably beyond the entreme frequencies of a predetermined range. By virtue of the common plate inductance il@ the two vacuumtubes are caused to oscillate together on a single compromise frequency.- lf

the oscillations are desired at a relatively low frequency it -is preferable'to use inductive feed back for the regeneration rather than the inter element capacity of the tubes as illustrated.

In order to accurately nx the natural fre-f quency .of each oscillator lll, if. resonant long Vlines 22, 2t for frequency control are coupled to the inductances i8, 2'0 included in the input cir cuits of -the oscillators.

As described in my copending application,.

Serial Number 400,4 89,' filed October 18, 1929, the long line is resonant, that is, it is left operi-n1 ended or-short .circuited so as to have standing --waves formed or produced thereon; The length lof line determines accurately the wave length of the standing waves formed. and they in turn. pull the oscillator into step therewith. y As the `lines maintain constant oscillation frequency within narrow limits, they will prevent unwanted frequency drift 4of the system which may often occur if the oscillators are of the ordinary type,

The frequency, at which the system so far described oscillates normally rwithout. the application of input energy, will be determined by the. circuits, and is some frequency between the frequencies at which tubes IU and l2 would each oscillate at if the other were made to cease drawing anode current. However, the frequency of oscillations occurring in lnductance coil llt is dependent upon the relative bias of the controlelectrodes l0, I2 and will approach more nearly the frequency, at any given instant, of that tube whose control electrode is biased relatively more positive lor, in other words, the frequency will 4be more nearly the natural frequency of the oscillator supplying'most energy. In another sense, therefore, the input circuit includlng transformer 8 is a frequency determining are alike, the frequency of energy appearing in coil IIS is that at which the two oscillators I0, I2 are forced to oscillate by virtue of their coupling through their common anode inductance.

The output of oscillators I0, I2 is fed, 'through the secondary of transformer IIB in phase opposition to the input electrodes of a carrier suppression modulator including electron dischargev devices 30, 32. High frequency energy from oscillator 34, preferably of the type disclosed in my copending application Serial Number 400,489, filed October 18, 1929 or of the type disclosed by James L. Finch and James W. Conklin in their copending application Serial Number 363,660, filed May 16, 1929, is fed to the input electrodes of tubes 30, 32 in parallel. Output energy of the modulator is supplied if desired, to a filter 35 for eliminating one side band appearing in the output circuits of devices 30, 32, and, the output of filter 34 is fed to a power amplifier and limiter 36 and then transmitted, for exarnple, by any suitable radiating antenna 38.

In Figure 2, molulating energy is fed from a source or land line 8 to the input circuit of two electron discharge devices I0, I2 having their anodes connected in pushpull or in phase opposition rather than cophasally as shownin Figure 1. As the oscillating circuit of Figure 2 is made up of the anode inductances, tube capacities and grid inductances it acts as a series tuned circuit and consequently there may be relatively little inductive feed back. i

Each of the oscillators I0, I2 has its frequency controlled by means of resonant long lines 22, 24 fixing the natural frequency of oscillators I0, I2 at or beyond the extreme frequencies of a desired range. Because of the close coupling of the anode and control electrode circuits, the entire system is forced to oscillate at some common intermediate frequency. The common or floating frequency is varied according to the biasing potentials applied to the secondary, of modulation transformer 42 connected to the control electrodes of tubes I0, I2 in phase opposition, the frequency approaching the natural frequency of that oscillator whose bias is altered positively so that the energy supplied by it appears in greater amount than that supplied by the other oscillator. If desired, frequency modulated energy from the oscillators I0, I2, is amplified b'y a sutl able power amplifier 44 and then radiated over any suitable radiating antenna 38. y

For a fuller discussion of the operation of the vunderlying principles of the frequency modulation oscillator tubes IIJ, I2, coupled together so asA to be forced to oscillate at a common frequency, reference is made to my United States Patent Number 1,787,979, Serial Number.264,'101 on Oscillation generation, filed March 23, 1928.

The long line used rfor frequency control need not be of the periodic or resonant type but may be. as shown in Figure 3, of aperiodic character, that is to say, of the type disclosed by James L. Finch and James W. Conklin in their copending application 363,660, filed May 16,'19279.

In Figure 3 aperiodic long line 22 which may be constructed in the form of a coil is coupled to the common tuned anode circuit `46 of screen grid tubes I0, I2 and to the tunedinput circuit 40 of electron discharge device oscillator I0.. The circuit 40 is grounded through a suitable condenser 46. The impedance of tuned circuit 40 -should be so adjusted to the currents from line- 22 that it equals the surge impedance of circuit. In the event that the bias on both tubes line 22 thereby insuring aperiodic transfer of energy from output circuit 46 to the input circuit 40. Anode potential is kept from the control electrode 48' of vacuum tube I0 by a suitable blocking condenser 50. To suitably bias the control electrode 48' of Vvacuum tube I0, a grid leak resistance 52 is provided. 'Iwo grid leaks, one for each tube, may also be used. To prevent interelectrode feed back and to insure feed back over long line 22 which is made approximately an odd number ofhalf wave lengths long taken at the frequency at which oscillator I0 is' desired to oscillate naturally; namely, at or beyond an eX- treme frequency of a desired range, screen grid 54 is provided, grounded for radio frequency currents by condenser 56 and supplied with Jsuitable biasing potential by the action of resistance 56. Provision is also made in building the equipment to provide for good electrical shielding between the anode circuit and the control grid circuits so that practically all the regeneration is from the energy carried back over the two long lines.

In addition, to further insure feed back solely through the long line feed back means provided,

the stages should be shielded from each other.

Circuits and elements are connected to oscillator I2 in a fashion similar to that described in connection with oscillator I0. The length of line 24 of oscillator I2 is chosen however, to be an odd number of half wave lengths .of a frequency f1 at the other end of the range of desired frequencies relative to the natural frequency of oscillator I D.

Because of the common anode circuit 46,

tuned to a frequency intermediate the oscillator 2 frequencies, both oscillators I0, I2 are forced to oscillate at some common, intermediate frequency. Modulation energy from 4transmitter 60 amplified by a suitable amplifier 62 and applied to the control electrodes of electron discharge devices I0, I2 through transformer 64,y

rality of cascaded tubes through aperiodic long lines to a preceding tube and wherein modulation voltages are applied to the screen grids of electron discharge devices rather than the control electrodes thereof. Modulation voltages appearing across resistance 10'v are fed in pushpull fashion to an amplifier 12 and then applied pushpull fashion through transformers 14, 'I6 in phase opposition to the control electrodes of p ushpull amplifier 18-having impedances, 82

in series with the anodes thereof The resulting amplified modulation voltages'j appearing across impedances 80, 82 areA applied to the screen grids of amplifiers 64, 86.

Tothe control electrodes of vacuum tubes 84, 86 are applied high frequency potentials, through aperiodic lines 88, 90, respectively, of

the type disclosed in the Finch and Conklin application referred/to. Modulated radio frequency output energy from electron discharge devices 84, 86 is fed to a tank'circuit 92 and thence through the input electrodes of a power amplifier 94 of the screen gridV type. Through 88 which represent e suitable unelss, eutput energy from the tuned plate circuit 98 of tube 94 .may be fed to an additional power amplifier 4before further transmission or radiation.

Feed back through lines 88, 90 occurs through connection |00 suitably shielded as shown.` As

the lines 88, 90 feed back energy from tube 84 which represents a second stage to 'tubes 84,.

first stage, they should,

for proper oscillation generation at the natural frequencies. be substantially an even number of half wave lengths long of the respective natural frequencies. Tank circuits 92 and 98 ,act as initial frequency determining circuits and force the Asystem to oscillate at an intermediate fre- `quency when no modulation biasing potentials .are appliedto thescreen grids 4of tubes 84, 86,

at which time the circuit including resistances 8 0, 82 becomes a frequency determining circuit.

Cathode energization and unidirectional biasing potentials for the various tubes are derived as indicated on the drawings. In order to test the voltage or current flowing in Aany part of the system test leads |02 are provided. 'A monitoring or listening in amplifier i'li of the pushvpull variety, by means of test-leads BOB allows of a check on the signal to be transmitted. In order to tunethe grid circuits of tubes 84, te tuning inductances i 88, HU are provided; and, grid leaks H2, lid maintain suitable biasing potentials on ythe control electrodes thereof. ln order to determine separately the anode currents flowing in each of tubes et, 88, the anode choke H6 is made in the form of a coil withl two parallel Wires in the winding having separately connected-ammeters' H8.

What I claim is:

1.v An arrangement for generating frequency wobbled oscillations comprising two electron emission tube oscillation generators having their input and output circuits shielded from each other, long lines coupling said circuitstogether for fixing their natural frequencies to or beyond the extreme frequencies of the desired range of frequency wobble, means coupling the oscilla-l tion generators together to force them to oscillate at a common frequency, and means for simultaneously oppositely wobblingthe bias of control electrodes of the tubes to oppositely vary the oscillation intensity in order to wobble the common frequency. I

2. An arrangement for generating frequency wobbled oscillations comprising two .screen grid `electron emission tube oscillation generators having their input and output circuits shielded from each other, long lines coupling said circuits together and fixing their natural frequencies to or beyond the vextreme frequencies of the desired range of frequency wobble, means coupling the oscillation generators together to force them to oscillate at a common frequency,

and means for Vsimultaneously oppositely vWobbling the bias of the screen grids of the tubes to oppositely vary the oscillation intensity in order to wobble the common frequency.

`'3. An arrangement for generating oscillations and frequency modulating the generated oscil- .lations in accordance with modulating energy l comprising'twov electron emission tube oscillation generators having input and output circuits shielded from each other, long llines coupling said circuits together and for xing `their natural frequency to or beyond the extreme frequencies of the desired frequency range, means coupling the oscillation generators together to cause them to oscillate at avcomrnon frequency, and means coupling the modulating energy to the control electrodes of tubes in phase opposition in order to oppositely vary their bias and consequently the oscillation intensity in order Y.

tubes in phase opposition in order to oppositely y vary their bias and consequently the oscillation .intensity in order to similarly vary the common frequency.

5. In radio signaling apparatus a transmitter comprising a. pair of screen grid electron discharge devices,` means for applying in phase opposition modulation energy to 4the screen grids of the devices,- means for applying high frequency energy to be modulated to the other grids of said devices and, a` tuned high frequency tank circuit lconnected rin parallel to th anodes and cathodes of said devices.

6. In radio signaling apparatus a transmitter comprising a plurality of high frequency stages, each stage comprising an electron discharge device having a pair of grids, means. for shielding the input and output circuit of each electron discharge device from each other, means for shieldingthe stages from each other, long line means vfor establishing high frequency feed back from one stage to another stage, and means for ap plying modulating energyto one of the grids of an electron discharge device in one of said' stages.

7. In radio ysignaling apparatus, a transmitter comprising a pair of high frequency stages, one of said stages comprising a pair of screen grid electron discharge devices, the other stage including a screen grid electron discharge device, means for shielding the output and input circuits of said electron discharge devices from each other, means for shielding the stages from each other, means for establishing feed back from one stage `to control electrodes of electron discharge devices forming another stage, and

means for applying modulating energy to the screen grids of said last mentioned electron discharge devices.

8. In apparatus of the character described, a pair of electron discharge device oscillator tubes, means coupling the tubes together' and feeding their output to an electron discharge device am- .plifler, a pair of long transmission lines coupling the output of said amplifier to the input circuits of said electron discharge device oscillator tubes each of said lines being of such a length as to cause each oscillator tube to operate at frequencies on opposite sides of a mean frequency when the other oscillator tube is rendered inoperative, and, means for modulating th:v

output of said electron discharge device oscillater tubes.

9. In electricalv apparatus a pair of electron discharge devices each havingan anode anathode and a control electrode, circuits intercon-v necting the control electrodes and cathodes and anodes and cathodes of said'devices.- the circuits for eachof said devices having inductance and capacity of 'such value that normally said devices tend to operate on opposite `sides of a -mean frequency, a long transmission line a plurality of half wave lengths long at a-frequency to one side of said mean frequency coupled to elecf trodes of one of said devices, said line tending to accurately fix the operating frequency of said device to said frequency at oneside of said' mean operating frequency," another long transmission line a plurality of half wave lengths long at a frequency lying to the other side of said mean frequency coupled to electrodes of said other electron discharge device, said last mentioned transmission line tending to cause said other device to operate accurately at said other frequency on said other side of said mean operating frequency, a plurality of said circuits being closely coupled together whereby said devices operate at said common mean frequency, and a circuit for oppositely varying the conductivity of said devices whereby the mean operating frequency of said devices shifts away from said mean frequency in accordance with the variation in conductivity of said devices.

l0. Apparatus as claimed in claim 9; and an inductor in each of said circuits for each of said devices, the transmission line for each of said tubesbeing coupled to at least one of said inductors.

11. Apparatus as claimed in claim` 9;. and a common output circuit for saidvdevices, said common output circuit having inductance and capacity and being tuned to thev mean operating frequency of said devices, the long lines being .connected from 'the common output circuit to the control electrode Vcathode circuits of said devices, and means for preventing the effects of interelectrode feed-back between the anodes and control electrodes of said devices.

12. Apparatus as claimed in claim 9, and a.

common output circuit for said devices, said common output circuit having inductance and capacity and being tuned to said mean frequency, each of said transmission lines being connected from said common output circuit to the control electrode cathode circuit of one of said devices, an impedance for terminating said lines, said impedance being connected between the output ends of said lines and the cathodcs of said devices, said terminating impedances being/I equivalent in value to the characteristic surge impedances of said lines,l and circuits connected to electrodes of said devices for preventing the effects of anode control-electrode feedback through said devices. j

13. In electric apparatus, a pair of electron discharge devices each having an anode a cathode and a control electrode, a circuit` having inductance and capacity tuned to a mean operating. frequency-connected between said' anodes and control electrodes, a circuit having inductance and capacity tuned to one side of said pedances equal in value to the characteristic impedance of said transmission lines connected between the controlelectrode ends of said lines and said cathodcs, circuits acting to prevent the effects of anode control electrode capacity of said devices, and, a circuit for varying oppositely the 'conductivity of said devices whereby the frequency of energy appearingv in said common anodeJcathode circuit varies through said mean frequency.

14. In electrical apparatus, a source of modulating potentials, a Vpair of pushpull connected electron discharge devices each having a lament a plate and a grid, a resistor'for connecting said plates in opposition, a circuit for applying said modulating potentials to said grids in opposition, a pair of vacuumtubes each having an anode a cathode a control electrode and a screen grid, connections applying the voltage variations across said resistors in relative phase opposition to said screen grids, a circuit having inductance and capacity connected between said .panodes and said cathodcs, an amplifier having within an hermetically sealed container an anode a cathode a control electrode and a screen grid, means coupling said circuit having inductance and capacity to the control electrode of said amplifier, means for grounding the screen grid of said amplifier for radio frequency poten.-

tials, a circuit tuned to a mean operating frean anode a cathode a screen grid and a control grid, a resistance circuit symmetrically connected between said screen grids, means for applying. audio frequency potentials effectively in.

shunt to said 'symmetricalb resistance circuit, means for subjecting said control .grids to high frequency potentials, and, a tuned high frequency circuit connected between said anodes connected in parallel and said cathodcs connected in parallel.

16; In a highfrequency signaling system, a pair of electron discharge devices each having anode cathode Vand 'control grid electrodes, a tuned high frequency circuit connected between said anodes and cathodcs, a vacuum tube ampliiler having'v an input circuit and a tuned output circuit, means coupling the input electrodes of said vacuum tube amplifier to the tuned circuit connected between the anodes and cathodcs of saidv electron discharge devices, and, a pair of transmission lines of different electrical length, each of said lines having uniformly distributed inductance and capacity connected between thel tuned output circuitof said vacuum tube ampli-A fier and control grids of said electron discharge devices for causing desired feed back suiiicient to engender in the tuned output circuit of said vacuum tube amplifier high frequency electrical oscillations.

17. Apparatus as claimed in claim 16 in con-1-v bination withmeans for varying the conductivity of said electron discharge devices at a signaling rate, thereby modulating the oscillations in the tuned output circuit of s aid vacuum. tube amplifier. Y

v 18. Apparatus as claimed in claim I8 wherein- "each of said devices is provided with ascreen grid, wherein af resistance circuit is connected betweensaid screen grids and wherein means are provided for causing variation in current iiow through said resistance circuit at a signaling rate whereby the oscillations in said tuned amplifier circuit are modulated in accordance with signals to be transmitted.

19. In a high frequency signaling system a pair of electron discharge devices each having anode cathode control gridv and screen grid electrodes, a high frequency circuit connected in parallel to said anode and cathode electrodes, a vacuum tube amplifier, means for coupling input electrodes of said vacuum tubev amplifier to said high frequency circuit, a tuned high frequency circuit connectedl between the output electrodes of said vacuum tube amplifier, a pair of transmission lines each having uniformly distributed inductance and capacity coupling the output circuit of said amplifier to the control grids of said electron .discharge devices whereby feed back occurs through said lines sufilcient to cause continuous oscillatory electrical currents t a tuned high frequency circuit connected in l' parallel to the anode and cathode electrodes of of high frequency to flow in said amplifier output circuit, and means for applying modulating potentials to the screen grid electrodes of said Y devices in order to modulate the oscillations in said tuned amplifier output circuit.

20. A system for' producing oscillations Vcomprising'a pair of electron discharge devices each having anode cathode and control grid electrodes,l a tuned high frequency circuit connected between the anode'and cathode electrodes of said devices, a vacuum tube amplifier, means for coupling input electrodes of said vacuum tube amplier to said tuned high frequency circuit, a tuned high frequency circuit connected between the output electrodes of said vacuum tube amplier, and, a pair of transmission lines of different electrical length and having substantially uniformly distributed inductanceand capacity coupling the tunedoutput circuit of said .amplifier to the control grid and cathode electrodes of said electron discharge devices.

21. Apparatus as claimed in claim 18 wherein there is provided in addition an'impedancev connected between the output end of each line and the cathodes of said devices, the impedances being substantially equal in value to the surge impedance of the lines to which they are respectively connected.

22. Apparatus as claimed in claim 18 wherein means are provided for applying modulating ,potentials to electrodes of said devices in order to modulate the oscillations appearing in the tuned output circuit of said amplifier.

23. in a high frequency system, a pair of electron discharge devices each `having anode cathode control grid and screen grid electrodes,

said devices, a vacuum tube amplifier having inputv electrodes and output electrodes, means coupling said tuned electron discharge device circuit to the input electrodes of said vacuum tube amplifier,l a tuned circuitconnected between the output electrodes of said vaccum tube amplifier, a pair of transmission lines each havlng substantially uniformly distributed inductance and capacity connected between said tuned amplifier output circuit andthe control grid electrodes of said electron. discharge devices.

impedances substantially equal to vthe surge impedances of the respective lines connected bevacuum tube amplier. Y

appearing in the tuned output circuit of said 15 CLARENCE WESTON 

